The efficiency of the restraint systems in vehicles will increase greatly in the future to further improve the protection of passengers in the vehicle. This means that the number of restraint devices and their respective deployment device in the vehicle will increase drastically. These restraint devices will then include, for example, airbags for the driver and front passenger, optionally deploying in multiple stages, knee bags for the driver and front passenger, side airbags for the driver, front passenger and rear passengers, with side airbags possibly being provided for the head area as well as the chest area, seat belt tensioners which may also be activated in multiple stages, possibly also rollover bars, etc. Thus, a complex safety system composed of multiple restraint devices will be installed in the vehicle for each occupant of the vehicle.
A complex restraint system is described in the article “Bussystem zur Vernetzung von Aktuatoren für Rückhaltesysteme” by J. Bauer, G. Mehler and W. Nitschke in the Conference Proceedings of the SAE International Congress & Exposition, Feb. 24-27, 1997 Detroit. Bulky wiring harnesses have been eliminated by the introduction of a bus system which networks all the restraint devices. With this known system, each restraint device has its own data processing unit having essentially a processing unit, data input and output circuits, a memory unit, a time and clock base and a power supply. This data processing unit, which is also referred to as a peripheral intelligent ignition power module, is arranged in immediate proximity to the deployment device belonging to the respective restraint device, namely in an ignitor cap or on a substrate of the ignitor itself.
From a central control unit, each data processing unit receives its power supply over a bus line. In addition, the central control unit determines on the basis of multiple sensor signals—e.g., acceleration sensors, precrash sensors, seat occupancy sensors—which restraint devices are to be deployed. Accordingly, the central control unit addresses the respective data processing units with the help of a protocol transmitted over the bus line. Diagnostic requests also go out over the bus line from the central control unit to the individual data processing units which send their diagnostic responses back to the central control unit over the bus line.
Due to the fact that all the data processing units are designed similarly, this yields a great flexibility in the design of the restraint system for different equipment variants.
The greater the number of data processing units networked over the bus and controlled by the central control unit, the more problematical is the implementation of real-time operation.
A similar restraint system, where the control of each restraint component (e.g., airbags, seat belt tensioners) is provided by a processor assigned to it, is known from German Published Patent Application No. 195 19 130. The processor assigned to each restraint component deploys that restraint component only when this processor receives a deployment command from a central electronic unit. Such a deployment command is generated by the central electronic unit as a function of crash sensor signals. The optimum reaction mode for the respective restraint component is calculated by the respective processor from signals from the seat position sensors, child seat detection sensors, seat occupancy sensors and seat belt sensors.